Wheel condition monitoring system

ABSTRACT

A wheel condition-monitoring system comprises transmitters ( 1 ) installed on individual rotatable wheels, for transmitting conditions of the wheels, and a receiver ( 11 ) installed on the side of a vehicle body, for receiving the conditions of the wheels sent from the transmitters. The rotation speed of the wheels are detected, and data that indicate the conditions of the wheels are sent from the transmitters ( 1 ) to the receiver ( 11 ) at intervals in accordance with the rotation speeds detected, or data that relate to a pressure etc. are sent for a predetermined number of times at a transmission interval of a first cycle that assumes a high speed range. At the same time, data transmission of a predetermined number of times corresponding to the transmission interval of the first cycle is repeated for a predetermined number of times at a transmission interval of a second cycle that assumes a low speed range and is longer than the first cycle. This increases reliability in data transmission and reception, and enables the system to function stably in the presence of a dead point.

TECHNICAL FIELD

The present invention relates to a wheel condition monitoring systemhaving a transmitter which is installed on an individual rotatable wheelto transmit the condition of the wheel, and a receiver which isinstalled on the vehicle body side to receive the condition of the wheelsent from the transmitter.

BACKGROUND ART

Conventionally, various types of systems for monitoring the condition ofa wheel have been known. One of the systems is, for example, a systemfor monitoring the internal pressure of a tire, which includes atransmitter consisting of a pressure sensor for detecting the internalpressure of tire, which is one of the conditions of wheel, and atransmission circuit for transmitting the pressure data, and a receiverconsisting of a receiving circuit for receiving the pressure data sentfrom the transmitter, and monitors the internal pressure of tire andgives an alarm etc. to the driver if abnormality is found. These wheelcondition monitoring systems are configured so that, taking the internalpressure of tire as an example, the pressure data from the pressuresensors installed on the individual wheels are sent from the individualtransmitters to one receiver installed on the vehicle body side. Theintensity of electric waves that are sent from the transmitter andreaches an antenna of the receiver changes in accordance with a changein position of the transmitter, which is caused by the rotation ofwheel. When the transmitter is present at a certain rotation angle, thereceiving intensity of electric waves at the receiver becomes low, sothat in some cases, a rotation angle at which the transmission andreception cannot be achieved is present.

FIG. 1 is a diagram for explaining one example of the send and receiveconditions in the above-described conventional wheel conditionmonitoring system. In the example shown in FIG. 1, the relative valuesof receive intensity are plotted for the rotation angle of wheel (360°for one turn of tire), and data can be transmitted and received stablyin a region on the outside of the receive limit. In FIG. 1, it is foundthat a dead point, at which the receive intensity does not reach thereceive limit is present at a right lower portion. FIG. 1 shows aconcept of one example, and the position of dead point or the presenceof dead point changes according to the tire size, data size, datatransmission speed, and the like. The above-described example has aproblem in that the demodulation of data is impossible at this deadpoint. In such a situation, the probability of achieving thetransmission and reception decreases, and hence the system does notfunction stably.

In order to eliminate the hindrance to the transmission and reception ofdata, which is caused by the above-described dead point, and to increasethe probability of transmission and reception, generally, the number oftimes of transmission has only to be increased. However, in the wheelcondition monitoring system relating to the present invention, if thenumber of times of transmission is increased excessively, there arises aproblem in that the following disadvantages are provided.

-   (1) An increase in the number of times of transmission accelerates    the run-down of battery, which shortens the life of transmitter.-   (2) An increase in the number of times of transmission causes the    transmission to overlap with the transmission of electric waves from    another tire in terms of time, which sometimes makes the reception    of data impossible.

It is an object of the present invention to provide a wheel conditionmonitoring system capable of performing a stable function of the systemby increasing the probability of the transmission and reception even inthe presence of a dead point.

DISCLOSURE OF THE INVENTION

The present invention has been made to achieve the above object, and theprincipal configuration and operation thereof are described below.

-   (1) The present invention provides a wheel condition monitoring    system having a transmitter which is installed on an individual    rotatable wheel to transmit a condition of the wheel and a receiver    which is installed on the vehicle body side to receive the condition    of the wheel sent from the transmitter, wherein the rotation speed    of the wheel is detected, and data indicating the condition of the    wheel are sent from the transmitter to the receiver at intervals in    accordance with the detected rotation speed of wheel.

According to this wheel condition monitoring system in accordance withthe present invention, the system is configured so that transmission isachieved at intervals corresponding to the rotation speed of wheel.Therefore, even if a dead point at which transmission and reception areimpossible is present, the probability that transmission and receptioncan be accomplished by several times of transmission can be increased,and the system can perform its functions stably.

-   (2) The present invention provides the wheel condition monitoring    system according to item (1), wherein when the receiver receives a    plurality of pieces of data sent from the transmitter installed on    each of a plurality of wheels, first data transmission from the    transmitter is performed after each waiting time set for each    transmitter has elapsed.

According to this wheel condition monitoring system in which the firstdata transmission from the transmitter is performed after each waitingtime set for each transmitter has elapsed, a problem in that thetransmission overlaps with the transmission of electric waves fromanother wheel in terms of time, which makes the reception of dataimpossible, arising if this invention is not applied, can be overcomesuitably.

-   (3) The present invention provides the wheel condition monitoring    system according to item (1) or (2), wherein the transmitter is    provided with an acceleration sensor, and the rotation speed of    wheel is determined from the measurement value of the acceleration    sensor.

According to this wheel condition monitoring system, by measuringcentrifugal acceleration acting on the outside in the radial directionby the acceleration sensor, the rotation speed of wheel can easily bedetermined from the already-known relationship between the rotationspeed of wheel and the measurement value of acceleration sensor, so thatthe present invention can be achieved suitably.

-   (4) The present invention provides the wheel condition monitoring    system according to any one of items (1) to (3), wherein a    transmission interval counter is provided; and a transmission    interval corresponding to acceleration determined by the    acceleration sensor is set in the transmission interval counter, the    transmission interval is counted until the set transmission interval    value becomes zero, and transmission is performed at the time when    the value becomes zero, by which transmission is achieved at    intervals in accordance with the rotation speed of wheel.

According to this wheel condition monitoring system in whichtransmission is achieved at the intervals corresponding to the rotationof wheel by utilizing the acceleration determined by the accelerationsensor and the transmission interval counter, transmission can beachieved suitably at the intervals corresponding to the rotation speedof wheel.

-   (5) The present invention provides the wheel condition monitoring    system according to any one of items (1) to (4), wherein a    transmission number counter is provided; and the number of times of    transmission, which has been determined in advance, is set in the    transmission number counter, the number of times of transmission is    counted until the set number of times of transmission becomes zero,    and transmission is finished at the time when the number of times of    transmission becomes zero.

According to this wheel condition monitoring system in which the numberof times of transmission is controlled by utilizing the transmissionnumber counter, the control of the number of times of transmission canbe carried out suitably.

-   (6) The present invention provides a wheel condition monitoring    system having a transmitter which is installed on an individual    rotatable wheel to transmit a condition of the wheel and a receiver    which is installed on the vehicle body side to receive the condition    of the wheel sent from the transmitter, wherein data that indicate    the condition of wheel are sent a predetermined number of times at a    transmission interval of a first cycle that assumes a high speed    range, and also data transmission of a predetermined number of times    at the transmission interval of the first cycle is repeated a    predetermined number of times at a transmission interval of a second    cycle that assumes a low speed range and is longer than the first    cycle.

According to this wheel condition monitoring system in accordance withthe present invention, a plurality of times of transmissions areperformed by combining two transmission intervals of the transmissioninterval of the first cycle that assumes a high speed range and thetransmission interval of the second cycle that assumes a low speed rangeand is longer than the first cycle. Therefore, even if a dead point atwhich transmission and reception are impossible is present, theprobability that transmission and reception can be accomplished byseveral times of transmission can be increased, and the system canperform its functions stably.

-   (7) The present invention provides the wheel condition monitoring    system according to item (6), wherein when the receiver receives a    plurality of pieces of data sent from the transmitter installed on    each of a plurality of wheels, first data transmission from the    transmitter is performed after each waiting time set for each    transmitter has elapsed.

According to this wheel condition monitoring system in which the firstdata transmission from the transmitter is performed after each waitingtime set for each transmitter has elapsed, a problem in that thetransmission overlaps with the transmission of electric waves fromanother wheel in terms of time, which makes the reception of dataimpossible, arising if this invention is not applied, can be overcomesuitably.

-   (8) The present invention provides the wheel condition monitoring    system according to item (6) or (7), wherein the system is    configured so that in the case where the number of times of    transmission in the first cycle is 2 or more, the first transmission    interval in the first cycle is not the same as the second    transmission interval in the first cycle.

According to this wheel condition monitoring system which is configuredso that the first transmission interval in the first cycle is not thesame as the second transmission interval in the first cycle, therandomness of transmission position of data transmission is increased,and the probability that any transmission position deviates from thedead point can be increased, so that a waste of transmission can beeliminated suitably.

-   (9) The present invention provides the wheel condition monitoring    system according to any one of items (6) to (8), wherein the system    is configured so that in the case where the number of times of    transmission in the second cycle is 2 or more, the first    transmission interval in the second cycle is not the same as the    second transmission interval in the second cycle.

According to this wheel condition monitoring system which is configuredso that the first transmission interval in the second cycle is not thesame as the second transmission interval in the second cycle, therandomness of transmission position of data transmission is increased,and the probability that any transmission position deviates from thedead point can be increased, so that a waste of transmission can beeliminated suitably.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram for explaining one example of the send and receiveconditions in a conventional wheel condition monitoring system;

FIG. 2 is a block diagram of configurations of a transmitter and areceiver, which are common to wheel condition monitoring systems inaccordance with first and second embodiments of the present invention;

FIG. 3 is a partially sectional view showing one example of a state inwhich a wheel condition monitoring system in accordance with a first orsecond embodiment is installed on a vehicle;

FIG. 4 is a flowchart for explaining one example of an actual operationof a wheel condition monitoring system in accordance with a firstembodiment;

FIG. 5 is a diagram for explaining one example of a transmission patternin a wheel condition monitoring system in accordance with a secondembodiment;

FIG. 6 is a diagram for explaining another example of a transmissionpattern in a wheel condition monitoring system in accordance with asecond embodiment; and

FIG. 7 is a diagram for explaining still another example of atransmission pattern in a wheel condition monitoring system inaccordance with a second embodiment.

BEST MODE FOR CARRYING OUT THE INVENTION

Two embodiments in accordance with the present invention will now bedescribed with reference to the accompanying drawings. First, aconfiguration common to these embodiments is described. FIGS. 2( a) and2(b) are block diagrams each showing a configuration of a transmitterand a receiver, which constitute a wheel condition monitoring system inaccordance with the present invention.

A transmitter 1 shown in FIG. 2( a) includes a pressure sensor 2 formeasuring the pressure in a tire, a temperature sensor 3 for measuringthe temperature in the tire, an acceleration sensor 4 for measuring theacceleration of the tire, a control circuit 5 which controls the datameasurement intervals in the pressure sensor 2, temperature sensor 3,and acceleration sensor 4 and processes the obtained pressure data,temperature data, and acceleration data, a transmission circuit 6 fortransmitting the output sent from the control circuit 5, and an antenna7 attached to the transmission circuit. The temperature sensor 3 isprovided if necessary. Also, the acceleration sensor 4 is essential in afirst embodiment, but is not essential in a second embodiment.

A receiver 11 shown in FIG. 2( b) includes an antenna 12, a receivingcircuit 13 for receiving electric waves including various data sent fromthe transmitter 1, a control circuit 14 for processing various datareceived by the receiving circuit 13, and a display unit 15 fordisplaying the data processed by the control circuit 14 to the driveretc.

FIG. 3 is a partially sectional view showing one example of a state inwhich the wheel condition monitoring system in accordance with thepresent invention is installed on a vehicle. In the example shown inFIG. 3, the transmitter 1 consisting of the pressure sensor 2, thetemperature sensor 3, the acceleration sensor 4, the control circuit 5,the transmission circuit 6, and the antenna 7, which constitutes thewheel condition monitoring system, is installed on a wheel 23 integrallywith a cylindrical valve stem 22 for injecting air into a tire 21. Also,on the vehicle body side, the receiver 11 consisting of the antenna 12,the receiving circuit 13, the control circuit 14, and the display unit15 is provided. In the wheel condition monitoring system in accordancewith the present invention, the transmitter 1 is installed on each ofthe wheels, and one receiver 11 which receives the pressure data etc.sent from the transmitter 1 and displays that data as necessary isprovided on the vehicle body side.

Of the above-described two embodiments having a common configuration,first, the first embodiment is explained below. In the wheel conditionmonitoring system of the first embodiment, as described above, when thedata of the internal pressure in tire etc. is sent from the transmitterto the receiver, the transmission intervals in the case where the samedata are transmitted a plurality of times are determined in accordancewith the rotation speed of wheel, by which the transmission/receptionefficiency is enhanced. Specifically, the rotation speed of wheel isdetected by the acceleration determined by the acceleration sensor inthe transmitter installed on the tire, and the data are sent attransmission intervals according to the detected rotation speed ofwheel.

As one example, Table 1 gives the results of the relationship betweenthe speed of vehicle, time for one rotation (inverse number of rotationspeed of wheel), and acceleration (G), which were obtained under theconditions of a tire size of 245/40ZR18, a rim size of 18×8 JJ, a tireoutside diameter of 653 (mm), a rim outside diameter of 457 (mm), andone circumference length of 2.05 (m).

TABLE 1 Speed of vehicle (km/h) 25 50 100 200 300 Time for one rotation(ms) 295.5 147.8 73.9 36.9 24.6 Acceleration (G) 11 42 169 675 1519

From the results shown in Table 1, it is found that the rotation speedof wheel correlates with the acceleration and further with the speed ofvehicle. Because of this fact, from the acceleration detected by theacceleration sensor installed on the wheel, the rotation speed of wheelis found based on the unequivocal relationship between the rotationspeed of wheel and the acceleration, so that the transmission intervalin accordance with the rotation speed of wheel can be determined.

FIG. 4 is a flowchart for explaining one example of an actual operationof the wheel condition monitoring system in accordance with the presentinvention. Hereunder, the wheel condition monitoring system of thisembodiment is explained by following the flowchart shown in FIG. 4.

First, the number of times of transmission for sending one same datadetermined by the pressure sensor etc. is set in a transmission numbercounter (Step 1). After waiting time set for each transmitter haselapsed (Step 2), the data determined by the pressure sensor etc. arefirst transmitted to the receiver together with the ID of transmitter(Step 3).

The reason why the first transmission is performed after the waitingtime set for each transmitter has elapsed is that if the firsttransmission is performed at the same time from a plurality oftransmitters, these transmissions overlap with each other, so that thefirst signal cannot be received at all by one receiver. Also, as thenumber of times of transmission to be set, a value of about 2 to 10 isselected in advance considering the tire diameter, vehicle speed, etc.according to the type of vehicle to which this system is applied. If thenumber of times of transmission becomes large, the probability ofsuccess of transmission and reception increases, but on the other hand,the run-down of battery for transmitter becomes heavy. Therefore, aproper value must be set based on past experiences.

Next, the acceleration a of a rotating tire is measured by theacceleration sensor (Step 4), and a value obtained by subtractingtransmission time from the transmission interval n corresponding to themeasured acceleration a is set in a transmission interval counter (Step5). The method for determining the transmission interval correspondingto acceleration a is explained later by giving one example. Here, thetransmission interval does not mean an interval between the finish oftransmission of certain data and the start of transmission of next data,but means an interval between the start time of transmission of certaindata including data transmission time and the start time of transmissionof next data.

Next, 1 is deducted from the value of transmission interval counter(Step 6), and it is judged whether or not the value of transmissioninterval counter is 0 (Step 7). As the result of judgment, if the valueof transmission interval counter is not 0, the control returns to thepoint between Step 5 and Step 6, and operations in Step 6 and Step 7 arerepeated. As the result of judgment, if the value of transmissioninterval counter is 0, the data of pressure etc. are transmitted (Step8). The transmitted data are transmitted as data of, for example, 48bits in which the transmitter ID and the pressure data, temperaturedata, and acceleration data are connected in a serial form.

Next, 1 is deducted from the value of transmission number counter (Step9), and it is judged whether or not the value of transmission numbercounter is 0 (Step 10). As the result of judgment, if the value oftransmission number counter is not 0, the control returns to the pointbetween Step 4 and Step 5, and operations in Step 5 to Step 10 arerepeated, by which the transmission of the same data is repeated. As theresult of judgment, if the value of transmission number counter is 0,the transmission of one same data finishes to prepare for thetransmission of next data.

The above-described operations in the wheel condition monitoring systemof this embodiment are carried out within the control circuit 5 of thetransmitter 1. Thereby, the system can be configured so that the data oftire pressure etc. are transmitted to the receiver 11 at intervalsaccording to the rotation speed of wheel.

Although as the method for determining the transmission intervalcorresponding to the acceleration a, various methods are possible, it ispreferable that time for one rotation of wheel be determined from theacceleration determined by the acceleration sensor from Table 1, and avalue obtained by dividing that time by (number of times oftransmission−1) be an integer so that all numbers of times oftransmissions set during this one rotation can be performed. Forexample, if the number of times of transmission is 5 and the value ofacceleration sensor is 42 (G), referring to Table 1, the transmissioninterval is preferably set so that transmission interval=time for onerotation/(number of times of transmission−1)=147.8/4=36.95≈37 (ms).Needless to say, if the size etc. of tire change, the data in Table 1changes accordingly, so that data matching the actual tire must be used.

Also, as another example of the method for determining the transmissioninterval corresponding to the acceleration a, it is also preferable thatas shown below, a range be set in the rotation speed, and a fixedtransmission interval be set for each of the set range. In the followingexample, the range is set and indicated according to the vehicle speedfor ease of explanation. However, as is apparent from theabove-described Table 1, the vehicle speed correlates with the rotationspeed of wheel, so that it is clear that the same as in the case wherethe range is set in the rotation speed is true. Also, the number oftimes of transmission is taken as M. Further, it is assumed that thevehicle speed is not equal to or higher than 300 km/h.

-   (a) Vehicle speed: 25 km/h or lower    -   Acceleration a<10 (G)→Time for one rotation: 300 (ms)    -   Transmission interval=300/(M−1) (ms)-   (b) Vehicle speed: 25 km/h to 50 km/h    -   0 (G)<Acceleration a<40 (G)→Time for one rotation corresponding        to 40 (G): 150 (ms)    -   Transmission interval=150/(M−1) (ms)-   (c) Vehicle speed: 50 km/h to 100 km/h    -   40 (G)<Acceleration a<170 (G)→Time for one rotation        corresponding to 170 (G): 75 (ms)    -   Transmission interval=75/(M−1) (ms)-   (d) Vehicle speed: 100 km/h to 200 km/h    -   170 (G)<Acceleration a<680 (G)    -   Time for one rotation corresponding to 680 (G): 40 (ms)    -   Transmission interval=40/(M−1) (ms)-   (e) Vehicle speed: 200 km/h to 300 km/h    -   680 (G)<Acceleration a<1500 (G)    -   Time for one rotation corresponding to 1500 (G): 25 (ms)    -   Transmission interval=25/(M−1) (ms)        In the above-described example, explanation has been given of        the measurement of condition such as the pressure in tire.        However, it is a matter of course that the wheel condition        monitoring system in accordance with the present invention can        be employed to measure the condition such as the internal        pressure of not only a tire but also a rotatable body. Also, in        the above-described example, as the condition to be measured in        a tire, pressure, temperature, and acceleration have been given        as one example. However, it is a matter of course that other        conditions of wheel, for example, data of rim vibrations etc.        can also be measured by installing a vibration sensor on the        transmitter.

Next, of the two embodiments having the above-described commonconfiguration, a second embodiment will be described. In the wheelcondition monitoring system of the second embodiment, when the data suchas pressure data is sent from the transmitter 1 to the receiver 11, aplurality of times of transmission is performed by combining twotransmission intervals of a transmission interval of a first cycle thatassumes a high speed range and a transmission interval of a second cyclethat assumes a low speed range and is longer than the first cycle, bywhich the transmission/reception efficiency is enhanced. The embodimentwas achieved by the study described below. In this consideration, thedesign upper limit speed was assumed to be 300 km/h. Also, in theexplanation given below, the term “transmission position” means therotation position of wheel during the time when data is sent from thewheel during rotation, and is the rotation position described as“transmission time” in FIG. 1.

(A) Speed 0 (Stop Time)

The reception probability at the stop time is the angle of deadpoint/360 because the rotation angle during transmission time is 0.Therefore, even if the transmission time and the number of times oftransmission are controlled, no improvement can be expected.

(B) High Speed Range (180 to 300 km/h)

The time required for one rotation of tire in this range is as short as22 to 40 ms. In order that, of the succeeding two transmissions, even ifthe transmission position of the first transmission overlaps with thedead point, the transmission position of the later transmission does notoverlap with the dead point appearing after one cycle, a shortertransmission interval (for example, 10 to 16 ms) easily improves thereception probability.

(C) Low speed range (30 km/h or Lower)

The low speed range is a range close to the stop time, for example,being 30 km/h. The time required for one rotation of tire is 250 ms. Inthis region, in order that, of the succeeding two transmissions, even ifthe transmission position of the first transmission overlaps with thedead point, the transmission position of the later transmission does notoverlap with the same dead point in the same cycle, the transmissioninterval should be as long as possible. On the other hand, if thetransmission interval is increased, the consumption of stand-by powerduring this time increases, and hence the run-down of battery cannot berestrained. Therefore, it is considered that three times of transmissionat transmission intervals of 100 to 150 ms are desirable. Here, thetransmission interval does not mean an interval between the finish oftransmission of certain data and the start of transmission of next data,but means an interval between the start time of transmission of certaindata including data transmission time and the start time of transmissionof next data.

(D) Medium Speed Range (30 to 180 km/h)

The medium speed range can be handled by combining transmission patternsin the low speed range and the high speed range without takingindividual measures.

From the above considerations, it is thought that the two transmissionintervals of the transmission interval of the first cycle that assumesthe high speed range and the transmission interval of the second cyclethat assumes the low speed range and is longer than the first cycle areadvantageous in efficiently increasing the reception probability.Concretely, a first cycle and a second cycle as described below arepossible. The example given below is one example, and it is apparentthat the present invention is not limited to this example.

(a) First Cycle

-   (1) The case where the number of times of transmission in the first    cycle is two (in the case where during two times of data    transmission, one transmission interval in the first cycle T1 is    present):

The first cycle assumes 300 km/h, which is the highest speed in design.Assuming that the tire size in which one rotation cycle of tire is theshortest is a size of 205/45ZR16 (external shape: 588 mm), which is thefinal external shape in accordance with the ZR standard, the time forone rotation of wheel in this case is 22.2 ms (300 km/h). Consideringthat the transmission time is 8 ms, a transmission interval T1 of 8 to22 ms is proper.8 ms<T1<22 msThe reason for this is that in order that both of the transmissionpositions of both transmissions do not overlap with the dead point, thetransmission interval must be equal to or shorter than 22 ms.

-   (2) The case where the number of times of transmission in the first    cycle is three (in the case where during three times of data    transmission, two transmission intervals in the first cycle T11 and    T12 are present):

In order that the third data transmission does not overlap with thefirst data transmission, the transmission intervals in the first cycleT11 and T12 of 8 to 11 ms are proper.8 ms<T11, T12<11 msAlso, in the case where the first transmission interval in the firstcycle T11 and the second transmission interval in the first cycle T12are different from each other, the probability that the transmissionposition of any transmission deviates from the dead point can beincreased when various vehicle speed conditions and various dead pointdistribution conditions are considered, so thatT12=T11+θis preferable.(b) Second Cycle

-   (1) The case where the number of times of transmission in the second    cycle is two (in the case where between two data transmission groups    of a predetermined number of times in the first cycle, one    transmission interval in the second cycle T2 is present)

The second cycle is set to increase the reception probability in a lowspeed range, and, as described above, is preferably 100 to 150 ms.

The following relation is possible.T2=T1×(N+0.5)In this equation, by making N an integer, and selecting N suitably, thevalue of T2 can be made 100 to 150 ms.

-   (2) The case where the number of times of transmission in the second    cycle is three (in the case where between three data transmission    groups of a predetermined number of times in the first cycle, two    transmission intervals in the second cycle T21, T22 are present):

The following relations are possible.T21=T1×(N+0.3), andT22=T1×(N+0.6)In this case as well, by making N an integer, and selecting N suitably,the values of T21 and T22 can be made 100 to 150 ms.

Examples of actual transmission patterns determined based on the aboveconsideration are shown in FIGS. 5 to 7 as Propositions 1 to 6. All ofthese propositions show actual values that can be adopted as the firstand second cycles in the wheel condition monitoring system of the secondembodiment.

In FIG. 5, as Proposition 1, an example is shown in which in the firstcycle, data transmissions are performed two times (one transmissioninterval in the first cycle is T1), and in the second cycle, two datatransmissions in the first cycle are performed two times (onetransmission interval in the second cycle is T2), and, as Proposition 2,an example is shown in which in the first cycle, data transmissions inthe first cycle are performed two times (one transmission interval inthe first cycle is T1), and in the second cycle, two data transmissionsin the first cycle are performed three times (two different transmissionintervals in the second cycle are T21 and T22).

In FIG. 6, as Proposition 3, an example is shown in which in the firstcycle, data transmission is performed three times (the two sametransmission intervals in the first cycle are T1), and in the secondcycle, three data transmissions in the first cycle are performed twotimes (one transmission interval in the second cycle is T2), and asproposition 4, an example is shown in which in the first cycle, datatransmission is performed three times (the two same transmissionintervals in the first cycle are T1), and in the second cycle, threedata transmissions in the first cycle are performed three times (twodifferent transmission intervals in the second cycle are T21 and T22).

In FIG. 7, as Proposition 5, an example is shown in which in the firstcycle, data transmission is performed three times (two differenttransmission intervals in the first cycle are T11 and T12), and in thesecond cycle, three data transmissions in the first cycle are preformedtwo times (one transmission interval in the second cycle is T2), and asProposition 6, in the first cycle, data transmission is performed threetimes (two different transmission intervals in the first cycle are T11and T12), and in the second cycle, three data transmissions in the firstcycle are performed three times (two different transmission intervals inthe second cycle are T21 and T22).

In the above-described examples, the measurement of conditions such aspressure in tire has been explained. However, it is a matter of coursethat the wheel condition monitoring system in accordance with thepresent invention can be employed to measure the conditions of not onlya wheel but also other rotatable bodies. Also, in the above-describedexample, pressure, temperature, and acceleration have been cited asexamples of conditions to be measured in a tire. However, it is a matterof course that the conditions of wheel other than these conditions, forexample, the data of rim vibrations can also be measured by installing avibration sensor on the transmitter.

INDUSTRIAL APPLICABILITY

As is apparent from the above description, according to the presentinvention, even if a dead point at which transmission and reception areimpossible is present, the probability that transmission and receptioncan be accomplished by several times of transmission can be increased,and the system can perform its functions stably.

1. A wheel condition monitoring system having a transmitter which isinstalled on an individual rotatable wheel to transmit a condition ofthe wheel and a receiver which is installed on the vehicle body side toreceive the condition of the wheel sent from said transmitter, wherein arotational speed of the wheel is detected, and data indicating thecondition of the wheel is sent from said transmitter to said receiver atintervals proportional to the detected rotational speed of the wheel. 2.The wheel condition monitoring system according to claim 1, wherein whensaid receiver receives a plurality of pieces of data sent from saidtransmitter installed on each of a plurality of wheels, first datatransmission from said transmitter is performed after each waiting timeset for each transmitter has elapsed.
 3. The wheel condition monitoringsystem according to claim 2, wherein said transmitter is provided withan acceleration sensor, and the rotation speed of wheel is determinedfrom the measurement value of said acceleration sensor.
 4. The wheelcondition monitoring system according to claim 2, wherein a transmissionnumber counter is provided; and the number of times of transmission,which has been determined in advance, is set in said transmission numbercounter, the number of times of transmission is counted until the setnumber of times of transmission becomes zero, and transmission isfinished at the time when the number of times of transmission becomeszero.
 5. The wheel condition monitoring system according to claim 1,wherein said transmitter is provided with an acceleration sensor, andthe rotation speed of wheel is determined from the measurement value ofsaid acceleration sensor.
 6. The wheel condition monitoring systemaccording to claim 5, wherein a transmission interval counter isprovided; and a transmission interval corresponding to accelerationdetermined by said acceleration sensor is set in said transmissioninterval counter, the transmission interval is counted until the settransmission interval value becomes zero, and transmission is performedat the time when said value becomes zero, by which transmission isachieved at intervals in accordance with the rotation speed of wheel. 7.The wheel condition monitoring system according to claim 6, wherein atransmission number counter is provided; and the number of times oftransmission, which has been determined in advance, is set in saidtransmission number counter, the number of times of transmission iscounted until the set number of times of transmission becomes zero, andtransmission is finished at the time when the number of times oftransmission becomes zero.
 8. The wheel condition monitoring systemaccording to claim 5, wherein a transmission number counter is provided;and the number of times of transmission, which has been determined inadvance, is set in said transmission number counter, the number of timesof transmission is counted until the set number of times of transmissionbecomes zero, and transmission is finished at the time when the numberof times of transmission becomes zero.
 9. The wheel condition monitoringsystem according to claim 1, wherein a transmission number counter isprovided; and the number of times of transmission, which has beendetermined in advance, is set in said transmission number counter, thenumber of times of transmission is counted until the set number of timesof transmission becomes zero, and transmission is finished at the timewhen the number of times of transmission becomes zero.
 10. A wheelcondition monitoring system having a transmitter which is installed onan individual rotatable wheel to transmit a condition of the wheel and areceiver which is installed on the vehicle body side to receive thecondition of the wheel sent from said transmitter, wherein data thatindicate the condition of wheel are sent a predetermined number of timesat a transmission interval of a first cycle that assumes a high speedrange, and also data transmission of a predetermined number of times atthe transmission interval of the first cycle is repeated a predeterminednumber of times at a transmission interval of a second cycle thatassumes a low speed range and is longer than the first cycle.
 11. Thewheel condition monitoring system according to claim 10, wherein whensaid receiver receives a plurality of pieces of data sent from saidtransmitter installed on each of a plurality of wheels, first datatransmission from said transmitter is performed after each waiting timeset for each transmitter has elapsed.
 12. The wheel condition monitoringsystem according to claim 11, wherein said system is configured so thatin the case where the number of times of transmission in the first cycleis 2 or more, the first transmission interval in the first cycle is notthe same as the second transmission interval in the first cycle.
 13. Thewheel condition monitoring system according to claim 11, wherein saidsystem is configured so that in the case where the number of times oftransmission in the second cycle is 2 or more, the first transmissioninterval in the second cycle is not the same as the second transmissioninterval in the second cycle.
 14. The wheel condition monitoring systemaccording to claim 10, wherein said system is configured so that in thecase where the number of times of transmission in the first cycle is 2or more, the first transmission interval in the first cycle is not thesame as the second transmission interval in the first cycle.
 15. Thewheel condition monitoring system according to claim 14, wherein saidsystem is configured so that in the case where the number of times oftransmission in the second cycle is 2 or more, the first transmissioninterval in the second cycle is not the same as the second transmissioninterval in the second cycle.
 16. The wheel condition monitoring systemaccording to claim 10, wherein said system is configured so that in thecase where the number of times of transmission in the second cycle is 2or more, the first transmission interval in the second cycle is not thesame as the second transmission interval in the second cycle.